There are three persons aged 60, 65 and 70 years old. The survival probabilities for these three persons for another 5 years are 0.7.0.4 and 0.2 respectively. What is the probability
that at least two of them would survive another five years?

Probability that at least two of them would survive another five years = 0.388

Step-by-step explanation:

We are given;

Probability of Survival of 60 years old for the next 5 years;

P(60 years old surviving) = 0.7  

Thus;

Probability of 60 years old not surviving for the next 5 years;

P(60 years old not surviving) = 1 - 0.7  = 0.3

Also,given;

Probability of Survival of 65 years old for the next 5 years;

P(65 years old surviving)  =  0.4  

Thus;

Probability of 65 years old not surviving for the next 5 years;

P(65 years not surviving)  =  1 - 0.4  = 0.6

Also,given;

Probability of Survival of 70 years old for the next 5 years;

P(70 years old surviving)  =  0.2  

Thus;

Probability of 70 years old not surviving for the next 5 years;

P(70 years not surviving)  =  1 - 0.2   = 0.8

Probability that at least two survived is;

P(at least 2 surviving) = [P(60 surviving) x P(65 surviving) x P(70 not surviving)] + [P(60 surviving) x P(65 not surviving) x P(70 surviving)] + [P(60 not surviving) x P(65 surviving) x P(70 surviving)] + [P(60 surviving) x P(65 surviving) x P(70 surviving)]

P(at least 2 surviving) = [(0.7)(0.4)(0.8)] + [(0.7)(0.6)(0.2)] + (0.3)(0.4)(0.2)  + [(0.7)(0.4)(0.2)]

P(at least 2 surviving) = 0.224  + 0.084  + 0.024 + 0.056

P(at least 2 surviving) = 0.388